A miniaturized flow-injection analysis (μFIA) system with on-line chemiluminescence detection for the determination of iron in estuarine water

A miniaturized flow-injection analysis system constructed from a glass base plate and polydimethylsiloxane (PDMS) top plate was employed for the determination of iron in river water. Two designs were investigated, one utilizing a syringe pump and the other utilizing EOF pumping with a mini-filtration system incorporated. The syringe pump system was used to optimize the analytical method on chip, where the pump was used to deliver both the analyte and the reagents to the reactor chip. The highly sensitive chemiluminescence reaction between alkaline luminol (3-aminophthalhydrazide) and 0.1 M of hydrogen peroxide (H2O2) in the presence of iron(II) was utilized. The bright blue light (λ max ∼ 440 nm) emitted was detected using a miniaturized photomultiplier tube interfaced directly under the chip. The light intensity signals were recorded, and the corresponding concentration of iron(II) concentration was determined. The calibration for iron(II) standards was linear up to 0.75 µg mL−1 (y = 5.7839x + 0.0378, r2 = 0.9939) with a precision value of up to 3.72% RSD, for n = 3. The limits of detection (blank + 3s y/x) were found to be 28 ng mL−1. The system which utilized EOF pumping and incorporated a minifiltration unit provided a linear calibration for 0–5 µg mL−1 (y = 3.316x + 0.1831; correlation coefficient, r 2 = 0.9996) over a working range of 0.0–0.5 µg mL−1. This system provided lower limits of detection 5.1 ng mL−1 and better repeatability (%RSD less than 0.5% for n = 4), but problems occurred with the mini-filtration system at higher iron(II) concentrations. The EOF pumping system provided slightly higher results for the concentration of iron(II) in the Humber estuary (0.058 µg mL−1), but these results were in line with the results expected by the Environment Agency.